What size tank are you keeping them in? Are there lots of plants/hiding places? I'm assuming their not siblings, that you purchased them at a store. When you say aggressive how do you mean; just chasing or attacking? They may be too young to sex but if you can post pics it might be possible.

When I had a problem with two females literally locking onto each other, I removed one & floated her in a non-see through bowl in the tank for a few hours then re-introduced her. They flared & puffed up but didn't attack any more, that was a 10g QT tank with 5 females total, lots of silk plants & a few caves.

I have a baby that just went through a growth spurt that is in with adult females and did fine. The biggest thing I noticed that helped was the baby was a very strong and fast swimmer. Two of the adult females are only about 4 months old and the other two are full grown females that are on the small side. One of the 4 month old and both full grown females are the friendliest girls in the tank. The only problem I had at first was that the runt was the most agressive and thought she was the alpha girl. The girls didn't really pay attention to her until she became too pesty. They finally put her in her place and now she hangs out with my two blue girls who are really friendly and get along with everyone in the tank. Now the girls are still working on getting the lavendar 4 month old to settle down. Every once in a while she gets worked up and starts chasing, but then after a day or so the girls will finally start chasing back until she settles down.

I think it all comes down to personality. I don't think I would reccommend putting a large female in with babies without knowing her personality because if she is too agressive she could easy injured or kill a baby.